The expansion of healthcare coverage through Medicaid will allow greater access to SUD treatment among those who currently do not have coverage. However, States will be concerned about cost containment as expansion of coverage will increase pressures on strained budgets. Health Homes (HHs) are a federally funded Medicaid program-authorized by the Affordable Care Act-to improve quality of care and reduce wasteful spending for chronic medical and behavioral conditions. HHs aim to increase patient centered care among the most vulnerable populations covered under Medicaid. New York (NY) has received federal approval and is currently rolling out its HH program statewide (anticipated enrollment of about 750,000). The NY HHs program has distinct features including a focus on SUD among enrollees with chronic medical and mental health disorders, fostering of local partnerships among diverse types of providers, and use of care managers to ensure patient centered care. Using a longitudinal design, this study will examine whether the NY HH program improves quality of care, reduces inefficient healthcare, and lowers costs among the 120,000/year individuals with SUD who are eligible for HHs in NY. Administrative data from 2006 through 2016 will be derived from a combination of Medicaid claims and encounters and SUD state registry records which include socio- demographics and substance use data. The study will occur in two phases. In the R21 Phase (1 Year), Primary Aims focus on putting a research infrastructure in place by establishing written agreements with state agencies, creating analytical datasets, and developing a statistical description of initial HH enrollees. Data analysi will include using descriptive and mixed effects logistic regression analyses to describe and contrast historical and baseline socio-demographic, clinical and healthcare utilization among subgroups (e.g., HH eligible with no SUD; high risk clients with SUD). In the R33 Phase (4 years), Primary Aims include examining whether HHs improve Medicaid quality indicators of SUD treatment, quality of medical and mental health care among SUD clients, efficiency of healthcare (e.g., avoidable rehospitalizations), as well as reduce Medicaid costs. Mixed effects logistic regression models will examine changes from historical rates of quality of care metrics and of costs while controlling for a variety of factors (e.g., individual clinically complicating factors). Generalized gamma models will be used to examine Medicaid costs by year. Secondary Aims focus on providing further evidence for making causal inferences about the effect of HHs on outcomes. Regression analyses will explore the relationship between HH program and quality and costs by comparing enrollees to statistically matched non-enrollees, examining the association between care manager activity and outcomes, and the association between moderators (e.g., homelessness) and mediators (e.g., primary care engagement) with efficiency and costs. Findings will have relevance as other states expand Medicaid coverage and use similar reform efforts for chronic conditions targeting the costliest and neediest populations.